Unsaturated rubbery polymers, such as diene type rubbers tend to exhibit poor aging characteristics and poor ozone resistance. These diene rubbers are commonly used in the formation of tire treads. Low unsaturation rubbers such as EPDM may be blended with diene rubbers to improve ozone resistance, but such blends exhibit increased hysteresis and reduced tensile strength and reduced modulus due to poor cure compatibility.
U.S. Pat. No. 3,915,907 to Roger J. Hopper, relates to chlorothio-sulfonamide-modified rubbery terpolymers having a low degree of unsaturation, mixtures of such modified terpolymers with highly unsaturated rubbery polymers and vulcanizates of such mixtures. As a result of improved cure compatibility, the vulcanizates showed superior properties and/or are particularly useful in the structure of pneumatic tire sidewalls. The modified rubbery terpolymers are prepared by reacting a terpolymer of ethylene, an .alpha.-olefin containing from 3 to 6 carbon atoms, and a non-conjugated diene containing from 6 to 12 carbon atoms with a N-chlorothio-sulfonamide. In a preferred embodiment, where the alpha-olefin is propylene, such terpolymers are commonly known as EPDM rubbers. The incorporation of the chlorothiosulfonamides into low unsaturated rubbery terpolymers can be achieved in a variety of ways such as by direct mixing, incorporation by swelling, or by reaction in solution. The rate of the reaction can be greatly accelerated by conducting it in the presence of a saturated aliphatic carboxylic acid containing from 6 to 30 carbon atoms, such as stearic acid. U.S. Pat. Nos. 4,820,780 and 4,910,266 to Roger J. Hopper relate to the use of such carboxylic acids.